Autonomic Drugs

Use this page to discuss and explain the important components/concept of autonomic drugs and the mechanism of their action.

Autonomic drugs that have effects similar to those of the effector agents in the two systems are called sympathomimetic and parasympathomimetic drugs
Drugs that mimic or block the effects of stimulation of the autonomic nervous system.

Basic concepts for naming ANS drugs:

l Acts where acetylcholine is released = cholinergic
l Acts where norepinephrine is released = adrenergic
l Acts at the location where PANS acts = parasympatho-
l Acts at the location where SANS acts = sympatho-


Direct- act on receptor
Indirect – inhibits cholinesterase -PANS stimulation

Cholinergic Agonists

Pharmacologic Effects:

• Eyes – Constricts the Pupils (Miosis), Cycloplegia and Decreased Intraocular Pressure
• Heart – Slows Heart Rate, Decreases BP, Cardiac Output, and Force of Constriction.
• Vascular Smooth Muscle - Vasodilation causing a fall in blood pressure.
• Bronchial Smooth Muscles - Constriction of Bronchioles
• Gastrointestinal Smooth Muscles – Excitation of GI Smooth Muscle; Sphincter is Relaxed.
• Secretory Glands - Stimulated
• Urinary Tract - Decreased Bladder Capacity

Adverse Effects:

• Large doses -> SLUD (Salivation-Lacrimation-Urination-Defication)
• Larger doses -> Neuromuscular Paralysis
• Toxic doses -> CNS Effects like Confusion

Therapeutic Uses:

• Glaucoma - Lowers Intraocular Pressure
• Xerostomia - Increases Salivary Flow
• Myasthenia Gravis (Weakness of Skeletal Muscles; Especially Ocular & Oropharyngeal) - Enhance Neuromuscular Transmission
• Antidote for Atropine Poisoning
• Paralytic Ileus and Bladder Atony - Stimulates Muscles Contractions in the GI System
• Dementia of Alzheimer's - Stimulates Cognition

Cholinergic agents can be direct (acting directly on the receptor) or indirect (causing a release of neurotransmitter which will then act on the receptor).

Antimuscarinic Drugs

1. atropine & scopolamine, naturally occurring alkaloids
2. homatropine, semisynthetic
3. Propantheline, synthetic quaternary ammonium
4. benztropine, synthetic non-quaternary ammonium

Pharmacologic Effects:

• Eyes – Dilates the Pupils (Mydriasis)
• Respiratory Tract - Relaxed Bronchial Smooth Muscle
• Secretory Glands - Xerostomia
• Gastrointestinal Smooth Muscles – Inhibit Motility
• Heart – Tachycardia
• Urinary Tract - Urinary Retention
• Body Temperature -Raised Due to Suppression of Sweat Glands.
• CNS - Decreases Stimulation; Drowsiness & Sedation.

General Uses:

• Opthalmology - Mydriasis to Exam Eyes
• Respiratory Tract - Bronchial Asthma
• Salivary Secretion - Diminish
• GI Tract - Treatment of Spasticity Syndromes
• Cardiovascular - Limited Use
• Urinary - Renal Colic; Over Active Bladder
• Preanesthetic Medication - For Sedation

Cholinergic transmission:
The conversion of choline to acetylcholine in the nerve terminal is accomplished by the enzyme choline acetyltransferase. The mitochondrial cofactor acetyl coenzyme A serves as the acetyl group donor for the reaction. The newly synthesized acetylcholine is then stored in the vesicles. The vesicles are transported toward the presynaptic membrane and make contact with specialized docking proteins, and the contents of the vesicles are released by exocytosis. Acetylcholine crosses the cleft in close proximity to Acetylcholinesterase (AChE). It is then hydrolyzed to choline and acetate at a rapid rate. The choline produced is then returned to the nerve terminal by a carrier mechanism and is once more used in the synthesis of acetylcholine.






Adrenergic Agonists

• Mimic effects caused by the stimulation of the sympathetic nervous system
• Activate adrenergic recptors
• Direct-acting agonist- directly binds to receptors to cause an effect
• Indirect-acting agonist- increases the amount of norepinephrine which will then cause the effect
• Receptors include: alpha 1, alpha 2, beta 1, beta 2 (G-protein linked receptors)
• Nuerotransmitters include: dopamine, norepinephrine, epinephrine (aka catecholamines)

Pharmacological effect

• Vascular effects

-constriction of vascular smooth muscle and vasoconstriction by stimulating alpha receptors

• Cardiac effects

-Norepinephrine and epinephrine stimulate beta receptors located on cardiac smooth muscle. This will increase the strength of the contraction and increases the work of the heart.

Therapeutic uses

• Local vasoconstriction (nasal decongestants, produce hemostasis, enhance local anesthesia)
• Tx of hypotension and shock (increase blood pressure by vasoconstriction)
• Bronchdilation (selective beta 2 agonists produce bronchodilation with less effect on the heart)
• Uterine relaxation (arrest premature labor by relaxing uterine smooth muscle)
• Reduction of intraocular pressure (reduce production ans enhance outflow of aqeous humor)
• Tx of allergic reactions (anaphylactic shock = IM of 0.4-0.6 ml of 1:1000 epinephrine)
• CNS stimulation (increase alertness and attention span and decrease sense of fatigue)

Therapuetic uses in Dentistry

• Vasoconstrictors

-prolong the duration of local anesthetic and may improve the frequency of successful nerve block
-toxicity of local anesthetic may be minimized by delaying and reducing the peak blood concentration of the local anesthetic
-when anesthic is given as infiltration, vasoconstrictors tend to reduce blood loss associated with surgical procedures